This invention relates to an electronic control circuit for controlling the operation of an audio amplifier, and more particularly, to a muting device utilized in conjunction with a telephone for controlling the operation of an audio amplifier. The circuit is activated automatically in response to the condition of the telephone line. While the invention is described with respect to such muting function, those skilled in the art will recognize the wider applicability of the inventive principles discussed hereinafter.
A number of devices for controlling radios or audio amplifiers, or for muting an audio amplifier are known in the art. Among the patents of which I am aware are Van Velsor, U.S. Pat. No. 2,498,349, issued Feb. 21, 1950, Butler, U.S. Pat. No. 2,503,095, issued Apr. 4, 1950, Hof, U.S. Pat. No. 2,792,450, issued May 14, 1957, Bloxsom, U.S. Pat. No. 3,267,379, issued Aug. 16, 1966, Ruthenberg, U.S. Pat. No. 3,328,695, issued June 27, 1967, Shaw, U.S. Pat. No. 3,446,976, issued May 27, 1969, and Ellis, U.S. Pat. No. 3,532,823, issued Oct. 6, 1970. In general, this body of prior art operates to automatically disconnect or connect a radio or similar audio device upon either the ringing of a telephone or the picking up of a handset for a telephone. That is the type of system disclosed in Van Velsor, Butler, Hof, and Ellis. Bloxsom discloses a device for the user of a mobile telephone to selectively use the telephone radio circuitry to control external equipment by dialing or otherwise manipulating a telephone apparatus. Ruthenberg is a transmitter/receiver unit in which the receiver output is muted during transmission. Shaw discloses an amplifier muting circuit based on telephone operation, but requires manual resetting of the audio amplifier after each use.
While this body of prior art has attempted to solve or provide a useful product for an intended purpose, the devices disclosed have not provided commercially successful because they are deficient in a number of respects. The devices generally are designed to permit controlled operation of a sound source, generally a "radio", during a telephone conversation. It is extremely convenient to permit a user to listen to an audio source at some desired level, and to mute that source when desired, as for example, when conducting a telephone conversation. As audio or "stereo" equipment has become more sophisticated, known devices have not functioned well when interconnected with those systems. Audiophiles spend relatively large sums of money in order to obtain pure, realistic sound reproduction. To my knowledge, devices prior to my invention either could damage operation of the audio equipment or cause distortion when interconnected with that equipment.
The invention disclosed hereinafter provides a compact, relatively low cost device which is designed for interconnection between a phone line and an audio amplifier to provide automatic muting of the audio circuit without distortion, and to permit return of the audio circuit to normal operation upon termination of phone usage.
One of the objects of this invention is to provide an improved audio muting circuit.
Another object of this invention is to provide a muting circuit which is compatible with a wide variety of audio amplifiers and phone circuits.
Still another object of this invention is to provide a muting circuit for audio amplifiers and phone circuits which is connectable to such circuits without requiring modification to those circuits.
Another object of this invention is to provide a low cost muting circuit design.
Another object of this invention is to provide a muting circuit design in which the only circuit components which are inserted in the audio path are resistive, so that no distortion of noise is introduced in the audio path.
Other objects of this invention will be apparent to those skilled in the art in light of the following description and accompanying drawings.